1. Field of the Invention
The present invention relates to an evaporation fuel processing system and a purging method therefor, which is equipped with a first communication passage through which an evaporation fuel generated inside of a fuel tank that stores fuel is introduced, a canister connected to the first passage and which adsorbs the evaporation fuel, a second communication passage that communicates between the canister and an intake passage of an internal combustion engine, and a purging processor for purging the evaporation fuel adsorbed by the canister into the internal combustion engine through the second communication passage.
2. Description of the Related Art
In order to supply fuel to an internal combustion engine, a fuel tank is used. Inside the fuel tank, an evaporation fuel (vapor), which is gassed out from the fuel, is generated. In order to prevent dispersion of the evaporation fuel into the atmosphere unnecessarily, a canister is provided.
The canister is filled with an adsorptive material such as activated carbon or the like, which adsorbs and collects the evaporation fuel. The collected evaporation fuel is purged into the intake passage of the internal combustion engine through a purging passage during running of the internal combustion engine. Owing thereto, breakthrough (outflowing) of the evaporation fuel from the canister drain is decreased.
Incidentally, there are times when after fuel has been filled into the fuel tank, running of the internal combustion engine may be stopped for long periods of time. In particular, with a hybrid system in which the internal combustion engine and an electric motor are used in common, there may be cases in which driving is performed only under operation of the motor, and where operation of the internal combustion engine is not conducted for a prolonged period.
At such times, inside the fuel tank, a large amount of evaporation fuel is easily generated, whereas the frequency of purging of evaporation fuel from the canister becomes quite small. As a result, cases occur in which the evaporation fuel, which cannot be collected by the canister, is simply released into the atmosphere.
Consequently, for example, as disclosed in Japanese Laid-Open Patent Publication No. 06-233410 (hereinafter referred to as Reference No. 1), a control apparatus for a generator-driving engine is known. In Reference No. 1, an electric vehicle is disclosed, having an engine that receives supply of fuel from a fuel tank and a generator, which is driven by mechanical output from the engine for generating electricity. In the control apparatus for controlling at least operations of the engine, there are disclosed, respectively, means for detecting the fuel vapor amount inside the fuel tank under a condition in which the engine is stopped, means for initiating driving of the engine in the case that the detected vapor amount exceeds a first predetermined amount, means for detecting the fuel vapor amount inside the fuel tank under a condition in which the engine is driven, and means for stopping the engine in the event that the detected vapor amount falls to or below a second predetermined value, the apparatus being characterized by the feature in that the second predetermined amount is smaller than the first predetermined amount.
However, when an internal combustion engine is not driven over a prolonged period of time, along with the passage of time, leakage of the evaporation fuel that has been adsorbed by the canister to the exterior occurs easily. Notwithstanding this fact, in the aforementioned Reference No. 1, purge processing is performed only upon detection of a fuel vapor amount inside the fuel tank. There is no disclosure of methods or practices for reducing breakthrough of evaporation fuel from a canister.